In applications such as ship hulls or bridge decks it has been known to increase the stiffness of steel plates by providing elongate stiffeners that comprise further steel girders welded perpendicularly to the main plate. The stiffeners may run in one direction or two orthogonal directions, depending on the forces to be borne by the plate. The use of stiffeners complicates the manufacturing process, adds significant weight and makes corrosion prevention and maintenance of the complete structure more difficult.
"Strength Evaluation of Novel Unidirectional-Girder-System Product Oil Carrier by Reliability Analysis" SNAME Transactions V93 1985 pp 55-77 describes an attempt to reduce the disadvantages of the provision of stiffeners in a ship hull by providing them only in one direction. This assists manufacture and maintenance of the ship to a certain extent but does not address other disadvantages of the provision of stiffeners.
Metal-plastic laminates with improved sound or heat insulating properties are known for use in cladding or roofing buildings, see for example U.S. Pat. No. 4,698,278. Such laminates generally employ foamed or fibrous materials and are not intended to, or capable of, bearing significant loads, i.e. significantly greater than self-weight and small loads due to localized wind or snow action.
U.S. Pat. No. 4,851,271 discloses the use of metal-plastic laminates to line oil pans to provide sound insulating properties. In such container applications the laminate as a whole will not bear loads significantly greater than self-weight and the container contents. Also, the lining layers do not contribute significantly to the structural strength of the laminate.
U.S. Pat. No. 5,219,629 discloses the use of aluminum sandwiches with a variety of core materials in the construction of truck trailer bodies. However, the aluminum layers are too thin and the core materials insufficiently strong to bear significant loads in larger structures.
"Behavior of Advanced Double Hull Sandwich Plate Systems: Experimental Investigation", a thesis by Josef Linder submitted in partial fulfillment of an M.Eng. at Carleton University, Ottawa, Canada, considered the use of a steel-polyurethane foam-steel sandwich for ship construction but concluded that it did not have sufficient flexural and bond strength nor sufficient energy absorption.